Vehicular guidance system with collision prevention

ABSTRACT

An improved installation for automatically guiding transportation vehicles along a track by means of a guide element defining and determining the track, wherein the improvement comprises means effectively preventing a collision of vehicles moving along the track at different speeds, without protruding into the path between the vehicles; the invention also comprises a guide rail and a transportation vehicle adapted to be used in such an installation.

United States Patent I72] Inventors Horst Schonbrodt Stemwarde/Hamburg; Volkmar Lining, Hamburg, both of, Germany [21] Appl. No. 714,927 [22] Filed Mar. 21, 1968 [45] Patented July 20, 1971 [73] Assignee H. .Iungheinricll & Co. Maschineniabrik Hamburg, Germany [32] Priority Mar. 23, 1967 [33] Germany 131 1 J 33 283 [S4] VEHICULAR GUIDANCE SYSTEM WITH COLLISION PREVENTION 5 Claims, 9 Drawing Figs.

[52] US. Cl 246/66, 343/l 12 R [5i] lnt.Cl B6ll23/l0 [50] Field of Search 246/187 C, 34 CT, 167, 63, 63 C, 8; 180/98; 340/33, 38 L, 32; 343/178, 112.4; 104/247 [56] References Cited UNITED STATES PATENTS 2,049,154 7/1936 Chireix 246/8 Primary Examiner-Arthur L. La Point Assistant Examiner-George H. Libman Att0rneyKarl F. Ross ABSTRACT: An improved installation for automatically guiding transportation vehicles along a track by means of a guide element defining and determining the track, wherein the improvement comprises means effectively preventing a collision of vehicles moving along the track at different speeds, without protruding into the path between the vehicles; the invention also comprises a guide rail and a transportation vehicle adapted to be used in such an installation.

VEIIICULAR GUIDANCE SYSTEM WITH COLLISION PREVENTION Our present invention relates to an installation for automatically guiding transportation vehicles, comprising a guide element determining the vehicular path. In a particularly preferred embodiment of this invention, this guide element is a rail, yet this is not an indispensable feature of the invention.

It is already known to provide an inductive or optical guide for automatic steering. In the first case, an electrical conductor system may be mounted either in or above the floor; in the second, a colored strip may be arranged on the floor. Where inductive guide means are provided, the control and steering means of the vehicle are connected to a receiver adapted to receive the electromagnetic signals from the conductor system. With optical guide means, at least one edge of the tape or strip is scanned by photoelectric cells or, particularly where the strip is made from a reflecting material, is swept by light beams transmitted from the vehicle with the reflection used for controlling the vehicle drive.

The invention encompasses all these arrangements; however, the preferred construction comprises a guide rail which may be U-shaped and is so fitted into the floor that its open side faces upwardly, the vehicle having a sensing wheel running in the channel of this rail.

A positive mechanical guide may, however, also be formed by a rail mounted above the track and above the floor; this modification is also within the scope of the invention.

The present invention also includes a transportation vehicle for use in an installation of this kind. ln accordance with the preferred embodiment just described, the vehicle is equipped with corresponding sensing rollers, or with transmitters and receivers for optical radiation or electrical energy, in order to guide the vehicle along the guide rail.

In order to define a track, such a guide rail may be designed with several curves. Frequently it will be mounted in bearings in the form of a closed track with a plurality of stations, where the vehicles may be loaded and unloaded.

Installations for positively guiding vehicles are already known, for example, from commonly owned German Pat. application No. 125531 ll/63c, German Pat. No. 3l2,l93, German Printed specification No. [,1 16,081, French Pat. No. 806,464, and U.S. Pat. No. 2,7l8,l94.

In these installations, there arises the problem that vehicles tend to travel at different speeds since, even with uniformly set drives, changes in speed will occur with all vehicles as a function of the load carried. In other systems, operating for example with points or switches and carrying out different programs for vehicle control, the vehicles cannot always be perfectly supervised, particularly where the execution of the program varies in duration.

It is therefore necessary to prevent damage to the vehicles caused by collisions or bumping," or preferably to avoid such collisions altogether. For preventing damage, bufferlike sensors can be provided, which deenergize the vehicle drive on encountering a resistance. For avoiding collisions, it has been proposed to equip the vehicles with a light source at one and with a light receiver at the other end. However, here the estimate of the distance along a straight track is rather uncertain and also the reliability of the interaction between light source and light receiver cannot be guaranteed, especially where vehicles travel along bends.

The invention has the object of providing an installation, in which, preferably with a continuous guide element, collisions of vehicles are reliably prevented without the use for any structure extending between the vehicles into their path, which would increase the risk of accidents.

According to the invention, this object is realized in that there are arranged, for sectional or block control, several oblong, electrically conducting elements arranged in sections at opposite sides of the guide element in staggered relationship overlap one another, with a central section of each conducting element crossing the laterally positioned guide element; the

sections of the conducting elements are longer than a selfpropelled vehicle traveling along the track. The vehicles are equipped, laterally of their longitudinal centerline, with a transmitter on one side and with a receiver on the other side, these transducers facing the juxtaposed conducting elements and being relatively offset to an extent corresponding to the mean spacing of these elements; the receiver controls or stops the vehicle drive as a function ofa signal. Speed control by intermittent actuation is also possible.

The guide element may also be mounted as a guide rail above the floor while the conducting elements are arranged in the floor, in which case the arrangement of the conducting elements on both sides of the guide element is determined by the vertical ground projection of this element. It is important that these elements be located, with regard to the path of the vehicle, with one section under one side of the vehicle and with the other section under the other side of the vehicle so that one section is associated with the transmitter and the other with the receiver, and a signal fed into the system by a transmitter of one vehicle is received by a receiver of another vehicle.

Preferably, the section associated with the transmitter, or with the transmitter side of the vehicle, leads in the direction of travel.

This arrangement solves in a surprising and unexpected manner the problem of preventing collisions, because a vehicle moving along a transmitter-side conductor section signals the receiver-side section immediately behind it to stop a vehicle entering the corresponding track portion.

A particularly advantageous embodiment of the invention provides for a contactless transmission of high frequency signals between the transmitter and the conducting element on the one hand, and between the conducting element and the receiver on the other hand, and the alternating energization of the transmitter and receiver of a vehicle, the transmitters of all vehicles operating on the same signaling frequency. The alternating energization has the object of preventing a vehicle from stopping itself, particularly with narrow spacing between transmitter and receiver, according to the width of the vehicle, or within the zone of a crossover of the conducting element over the guide element.

According to a further preferred feature of the invention, controls are provided for differently adjusting the rhythm of alternating transmitting and receiving periods on different vehicles. This is a safety measure in order to prevent the alternating transmitting and receiving periods of successive vehicles from being in complete synchronism; the different operating rhythms cause always a certain overlap between the transmission and reception periods of successive vehicles.

Advantageously, the conducting elements are closed conductor loops, into which a signal in inductively transmitted. These loops may be identically constructed sections on both sides of the guide element. In a preferred embodiment, the conductor loop in the section trailing in the direction of travel, arranged on the side on which the vehicles are equipped with the receivers, is narrower in front of the crossover point, with the conductors more closely spaced.

A preferably adjustable capacitor is advantageously mounted in every conductor loop for tuning it to the signal frequencies. Since all transmitters must be set to operate at the same frequency, the conductor loops must be matched to the resonance frequency in order to reduce energy consumption. Certain deviations in the conductor loops may result from tolerances during the assembly or from ambient conditions. In a simple arrangement, adjacent conductors of different loops are arranged in sections side by side and are accommodated in the same floor groove.

According to yet another embodiment for the contactless transmission of HF signals, the conducting element is a strip, and a capacitive coupling is provided between transmitter and strip on the one hand and between receiver and strip on the other hand. According to the construction of the receiver and transmitter, it might be advantageous to provide in this case a wireless return path by means of antennae arranged at the transmitter and receiver.

According to a further embodiment of the invention, the conducting elements are rails mounted immediately adjacent to the guide element made of conducting material, and the transmitter and receiver have each a pair of sensors scanning, respectively, the rail and the guide element, the transmitter feeding in a voltage and the receiver extracting a voltage. The guide element may here be a grounded terminal.

In the preferred physical realization of the installation according to the invention, the conducting elements are arranged in or at least on the floor and the guide element is also arranged on the floor, and the conducting elements are insulated against the guide elements at the crossing points. In this way a contactless arrangement is provided, particularly where the conducting elements are arranged to form a loop, in which no switching or transmission apparatus is necessary, apart from the closed loops in the floor or in the zone of the floormounted installation. Furthermore, this installation makes do with an extraordinarily low input, because of the small distance between transmitter and receiver, on the one hand, and conductor-loop conductors on the other hand, and the loop can, at least in part, be sufficiently separated to receive substantial energy levels in view of the directive transmission of the signals.

According to a further feature of the invention, the conducting elements may be provided with a tap and may be connected with a signaling device. Such a device may be a track layout on which the positions of the vehicles are indicated by lamps. Moreover, the signaling device may also be immediately adjacent to a device, e.g. where the track crosses a corridor. The warning device may be connected to an automatic barrier, as known per se. Furthermore, door-opening mechanisms may be operated in this manner by a tap on a conductor loop on the approach of a vehicle. Obviously, amplifiers may be inserted between the conductor loop and an operating mechanism.

According to yet another feature, the tap is a transmitter which is energized by the presence of electrical energy at or in the conducting element.

In the case of the preferred embodiment, in which the guide element is a floor-mounted rail for the sensor roller, and also the conducting elements are fitted into the floor, the invention provides that the guide rail is connected to an elongated, conductive element, mounted over a section of its length on one side and over another section of its length on the other side of the guide rail in isolated relationship therewith, crossing the rail between these sections in an insulated manner. Hence, such an installation may be easily assembled, because these rail parts may be embedded in the floor in one operation.

On the floor of a transportation vehicle, having the abovementioned equipment for being guided along such an element, there are provided. in the preferred embodiment a transmitter and a receiver on opposite sides of its longitudinal axis, the vehicle being further equipped with an automatic control for the alternating intermittent operation of transmitter and receiver; a switching mechanism for the vehicle drive is actuated as a function ofa signal received by the receiver.

The invention will be further described, by way of example, with reference to preferred embodiments diagrammatically illustrated in the accompanying drawing which shows only the features necessary for understanding the same.

In the drawing:

FIG. 1 shows the principle of alternating control, using a conductor loop as a conducting element;

FIG. 2 is a top view of a track section with several tapped conductor loops;

FIG. 3 is a top view of another embodiment ofa conductor loop;

FIG. 4 shows a track section underlying a conductor loop with two vehicles;

FIG. Sis a top view ofa track section with a strip for capacitive coupling;

FIG. 6 is a top view of an arrangement for mechanical sensing;

FIG. 7 is a diagrammatic side elevation ofa vehicle;

FIG. 8 is an end view of the vehicle of FIG. 7; and

FIG. 9 are diagrammatic graphs of the receiving and transmitting characteristics for different vehicles.

FIG. 1 shows an endless conductor loop 1 arranged not according to the invention but rectilincarly. A transmitter 2 is located at one end and a receiver 3 on the other end. Both transmitter and receiver include antennae of the ferrite type, these antennae being located substantially near the loop and so directed as to induce signals in the loop or to extract signals therefrom by inductive means. When the transmitter transmits high frequency signals, corresponding signals are received by the receiver 3. It should be remembered that the transmitter 2 and the receiver 3 are located in different vehicles proceeding in the direction of the conductor loop. For these high frequency signals frequencies of the order of magnitude of 500 c/s up to about 40 kc./s. are suitable Obviously, the conductor loop 1 serving as a coupling member between the transmitter 2 and the receiver 3 may be so tuned as to produce resonance for a selected frequency. For this reason, where corresponding values do not result from the design of the loop itself, tuning means are preferably fitted in the conductor loop.

The receiver 3 mounted on a vehicle is connected by connecting means 4 to an actuating member 5 which actuatcs a control device 6 adapted to stop the drive motor of the vehicle. If this drive motor 7 is an electric motor, the control device 6 may be a switch inserted in the motor circuit.

The parts 2 to 7 are located on a vehicle such as those shown in FIG. 4 at 29, 32 or in FIG. 6 at 40, 48. Naturally, the transmitter 2 and the receiver 3 are also connected via connections 76, 77 to an energy source 78 for supplying power thereto; this power supply is included in unit 66 shown in FIGS, 7 and 8 which controls the alternating switching of transmitter and receiver.

FIG. 2 shows the improved construction, according to the invention, of conductor loops disposed along a track. The track may be defined, for example, by a U-rail 8 open at the top and mounted in the floor; a sensor wheel runs in this rail 8 for steering the vehicle. The loop, shown generally at 9, has one section 10 on one side of the guide rail and another sec tion II on the other side thereof. Both sections extend parallel to the guide rail which is crossed by the two conductors l3 and 14 of the loop. If the guide rail is of conducting material, the crossover must be perfectly insulated.

In the sections 10 and 11, the two conductors l3, 14 are spaced from each other by a certain distance of, for example, about ll to 17 inches. The conductor located immediately next to the guide rail may also be slightly spaced therefrom. The spacing and the width of the conductor loops are so dimensioned as to enable a good coupling with the transmitter and receiver to be established, as will be further described with reference to FIG. 4. If the conductor loop contains at 15 a transmitter aboard a vehicle 1 moving in the direction of the arrow 16, the conductor loop will transmit a signal to a receiver 17 aboard a following vehicle 2 whereby the same is stopped in response to the signal received. This effectively prevents a collision.

As is apparent from a study of FIG. 2, the track is subdivided by the conductor loops 9, I8, 19, overlappingly disposed on opposite sides of the guide rail 8, into individual track sections in which the monitoring of approaching vehicles is carried out. Suitable dimensioning of the conducting elements 9, l8, l9 prevents the control action of one vehicle from extending unrestrictedly over the whole track. On the other hand, owing to the overlap, the collision protection extends practically without break over the entire track. Another advantage is that the amount of energy required for the control is small, because it serves only for transmitting a signal over a limited track section, corresponding to the length of a loop 9.

Since every vehicle is equipped with a transmitter and a receiver, transversely spaced from each other, in order to avoid that the receiver be affected by the transmitter mounted on the same vehicle, the aforementioned intermittent control can be carried out so that also a certain crosstalk, for example from the section of loop 9 to section of loop 19, remains ineffective.

FIG. 3 shows an arrangement which requires less coupling energy. If, according to FIG. 2, the upper sections of the conductor loops (as viewed in these FIGURES) are associated with the transmitter, then, as shown, for example for the conductor loop 21, the transmitter-side loop section 22 has a uniform width over its length whilst the receiver-side section 23 is narrower in front of the crossover, i.e. with a smaller distance between the conductors 25, 26. At the rearward end 27, the section 23 has again a greater width, in order to accomplish a good inductive coupling with the receiver of any following vehicle whenever the conductor loop 21 carries signals. When the vehicle passes beyond the crossover point 24, a following vehicle will be stopped when reaching the left end of the section 23 of the conductor loop. It follows from the preceding that the conductor loop sections must have the length of a vehicle or train. If the preceding vehicle is till in front of the crossover at 24, a following vehicle will be stopped by the signal transmission via the conductor loop 28.

A pair of vehicles moving over a conductor loop such as loop 9 of FIG. 2 are shown, by way of example, in FIG. 4. It may be seen that a preceding, first vehicle 29 has on its left side a transmitter 30 and on its right side a receiver 31. The second, trailing vehicle has on its left side a transmitter 33 and on its right a receiver 34. In the embodiment shown, the conductor loop has a length several times that of the vehicle. This greater length is to be preferred because it enables trailers to be pulled by the vehicles. The vehicles travel by means of wheels on the floor in which the guide rail 8 is mounted. A sensor roller runs in the rail 8, as will be subsequently explaincd with reference to FIG. 7. The leading vehicle 29 moves with its transmitter 30 over the section 10 of the loop 9 and induces therein a signal. When the vehicle 32 reaches the zone of the loop section 11, its receiver 34, tuned to the same frequency, receives this signal and stops the vehicle 32.

It should be stressed at this point that a conductor loop is not limited to the use of one turn winding. Several turns may be arranged in the manner of conductors l3, 14. FIG. 4 also shows a turning capacitor 35 in the conductor loop 9, whereby resonance with the transmitted signals may be achieved.

In FIG. 5, strips of conducting material 37 are mounted on either side of a sunken guide rail 36. These strips have a shape, with regard to the guide rail 36, conforming to the area of the loop 9 in FIG. 2. For a capacitive transmission of the signals, the use of strips is recommended.

FIG. 6 shows a track section similar to that of FIG. 4. A floor-mounted guide rail 38, cooperating with a sensor wheel, is associated with a conducting element 39, also in the form of a rail. The guide rail 38 consists of conducting material.

In this arrangement. the principle of the crossover of the conducting element 38 over the rail 39 is maintained and the scanning is effected with a pair of scanners on the transmitter and receiver. Thus, the vehicle 40 may have three sensors 41, 42, 43, of which the sensor 42 is associated both with the transmitter 44 and with the receiver 45. This scanner 42, for example in the form of a brush, sweeps along the guide rail 38, whilst the other scanners 41 and 43 engage either the section 46 on one side or the section 47 on the other side of the guide rail 38. FIG. 6 shows on the vehicle 40 the connections 79, 80 for the central sensor 42, one connector 80 leading to the receiver whereas the other connector 79 extends to the transmitter 44. This transmitter is connected by a connector 81 to the sensor 41, the receiver 45 being connected by a connector 82 to the sensor 43.

For the other vehicle 48, the corresponding connections between transmitter 49 and receiver 50, on the one hand, and the central sensor 52, on the other hand are shown'at 83, 84; the links between the receiver 50 and the sensor 53 are designated 83, the connection between the transmitter 49 and the sensor 51 being indicated at 86.

The transmitter 44 of the vehicle 40 applies a voltage signal to the conductor system formed by the guide rail section 38 and the conducting element 39. When a trailing vehicle with a corresponding arrangement of transmitter 49 and receiver 50, as well as sensors 51, 52, 53, reaches the conducting element 39, its brushes 52, 53 pick up the signal and apply it to the receiver 50 which causes the vehicle to stop in response to the received signal.

FIG. 6 shows also a track section for an installation according to the invention. This track section consists of a section of the guide rail 38 and the conducting element 39 insulatedly secured at 54 to the guide rail 38; it may also be mounted by insulating spacers 55, 56, 57 on further sections of the guide rail 38. This track unit may be mounted in the floor in one operation.

The vehicle according to FIGS. 7 and 8 has at its front end a forwardly directed, pole-shaped arm 59 with a sensor roller 60, which runs in the channel formed by the U-shaped guide rail. Inside the vehicle, the rising of the polelike arm is transmitted via a steering mechanism 6] to the front wheels 62, 63, as is known per se. In addition, the vehicle has, for example, at 64 a transmitter and at 65 a receiver. The antennae of these apparatus are directed towards the vehicle bottom lying about 2 to 3 inches above the floor level on which the vehicle travels so that there is a comparatively tight coupling with the conducting element, e.g. a loop according to FIGS. 2 to 4, located in the floor. If an embodiment according to FIG. 6 is used, the sensors project downwardly and brush the floor or the rails.

Transmitter and receiver are connected by a switchover unit 66, comprising, for example, a multivibrator, controlling the alternating energization of the transmitter and receiver and also containing switching means not shown in order to stop the drive motor 67 of the vehicle on reception of a signal by the receiver.

For example, in the vehicle shown in FIG. 7, a connection 103 leads from the switchover unit 66 to an additional front antenna 104, and a connection 105 to a rear antenna 106, these antennae supplementing the downwardly directed antenna elements of the transmitter and receiver. One such antenna element is shown at 107. The antennae 104 and 106 serve to form a wireless return path between the various vehicles, the connectors I03 and 105 being directed by the unit 66 towards the receiver or the transmitter. This construction is recommended for a capacitive coupling between the transmitter and a conductor strip on the one hand, and between the receiver and the strip on the other hand, an example of the positioning of the conducting elements being given in FIG. 5.

FIG. 2 shows another construction. By way of example, the conductor loops 9, l8 and 19 have taps 68, 69 and 70. These taps may be connected by leads 71, 72 to a track diagram or layout 73 which has a signal lamp for every track section defined by a conductor loop, so that the position ofevery vehicle can be indicated. The track diagram 73 is a stationary signaling equipment, arranged adjacent to the guide track for the vehicles. The leads 71, 72 may contain amplifiers or the like, or the taps 68, 69 may be constructed as transmitters.

The example of the tap 70, which may also be constructed as a transmitter, shows that the connecting means coming from the tap and shown at 74 lead to a stationary signaling or alarm device 75 for a warning system or for a door, in order to actuate the same upon the arrival of a vehicle at the loop 19 when the transmitter applies a signal to this loop.

FIG. 9 shows at 87 the transmitting and receiving characteristics of a first vehicle, and at 88 the transmission and reception times of a second or further vehicle in the system.

With reference to the abscissa 89, 90 the upwardly pointing arrows 91, 92 denote the shapes of the transmission pulses whereas the downwardly pointing arrows 93, 94 indicate the shapes of the received pulses. It can be seen that the outgoing pulses 95, 96 and 97, 98 alternate with incoming pulses 99, I00 and 10] 102, respectively. These pulses can be formed by frequency modulation for transmission and by intermittent energization for reception. It will also be seen that the pulses may have the same basic rectangular shape, but that the rhythm or duration of the pulses differs for both vehicles. For example, the pulses 95, 96 or 99, 100 of one vehicle may be twice as long as the pulses 97, 98, and 101, 102 of the other vehicle, i.e. are harmonically related thereto, so that different vehicles can reliably receive the pulses transmitted from other vehicles.

We claim:

1. A vehicular guidance system comprising:

elongated guide means forming a track;

a plurality of self-propelled vehicles provided with drive means and with sensing means for said track;

transmitting means and receiving means for high-frequency electrical signals aboard each vehicle, said transmitting means being disposed on a first side and said receiving means being disposed on a second side of said track upon alignment of the vehicle therewith;

a plurality of conductive elements disposed along said track in mutually insulated and longitudinally staggered relationship, each of said elements including a first portion extending alongside the track at said first side for energization by reactive coupling with said transmitting means of a passing vehicle, a second portion extending alongside the track at said second side in reactively coupled relationship with said receiving means of a passing vehicle, and a connecting portion crossing said track, said first portion preceding said second portion in the direction of vehicle motion and being substantially aligned with the second portion of an adjoining element, said conductive elements being strips capacitively coupled with said transmitting and receiving means;

switchover means aboard each vehicle for making said transmitting and receiving means alternately effective in a predetermined rhythm at harmonically related frequencies different for each vehicle whereby a signal picked up by said first portion of any conductive element from the transmitting means of a leading vehicle is communicated by said second portion thereof to the receiving means ofa trailing vehicle immediately behind, the length of each of said first and second portions exceeding that of each vehicle; and

control means aboard each vehicle connected to said receiving means thereof and responsive to said signal for arresting said drive means.

2. A system as defined in claim I wherein said transmitting and receiving means are provided with antenna means for establishing between two vehicles a return path for said signals.

3. A system as defined in claim 1, further comprising signalresponsive indicator means positioned next to said track and connected to at least one of said conductive elements for energization thereby upon passage ofa vehicle thcreover.

4. A vehicular guidance system comprising:

elongated guide means forming a track;

a plurality of self-propelled vehicles provided with drive means and with sensing means for said track;

transmitting means and receiving means for high-frequency electrical signals aboard each vehicle, said transmitting means being disposed on a first side and said receiving means being disposed on a second side of said track upon alignment of the vehicle therewith;

a plurality of conductive strips disposed along said track in mutually insulated and longitudinally staggered relationship, each of said strips including a first portion extending alongside the track at said first side for energization by capacitive coupling with said transmitting means of a passing vehicle, a second portion extending alongside the track at said second side in capacitively coupled relationship with said receiving means of a passing vehicle, and a connecting portion crossing said track, said first portion preceding said second portion in the direction of vehicle motion and being substantially aligned with the second portion of an adjoining strip, said transmitting and receiving means being provided with respective antennas at opposite ends of each vehicle for establishing between two closely spaced vehicles a return path for said signals independent of said conductive strips;

switchover means aboard each vehicle for making said transmitting and receiving means alternately effective in a predetermined rhythm different for each vehicle whereby a signal picked up by said first portion of any conductive strip from the transmitting means of a leading vehicle is communicated by said second portion thereof to the receiving means of a trailing vehicle immediately behind, the length of each of said first and second portions exceeding that of each vehicle; and

control means aboard each vehicle connected to said receiving means thereof and responsive to said signal for arresting said drive means.

5. A system as defined in claim 4 wherein said switchover means of different vehicles are pulse generators with harmonically related operating frequencies. 

1. A vehicular guidance system comprising: elongated guide means forming a track; a plurality of self-propelled vehicles provided with drive means and with sensing means for said track; transmitting means and receiving means for high-frequency electrical signals aboard each vehicle, said transmitting means being disposed on a first side and said receiving means being disposed on a second side of said track upon alignment of the vehicle therewith; a plurality of conductive elements disposed along said track in mutually insulated and longitudinally staggered relationship, each of said elements including a first portion extending alongside the track at said first side for energization by reacTive coupling with said transmitting means of a passing vehicle, a second portion extending alongside the track at said second side in reactively coupled relationship with said receiving means of a passing vehicle, and a connecting portion crossing said track, said first portion preceding said second portion in the direction of vehicle motion and being substantially aligned with the second portion of an adjoining element, said conductive elements being strips capacitively coupled with said transmitting and receiving means; switchover means aboard each vehicle for making said transmitting and receiving means alternately effective in a predetermined rhythm at harmonically related frequencies different for each vehicle whereby a signal picked up by said first portion of any conductive element from the transmitting means of a leading vehicle is communicated by said second portion thereof to the receiving means of a trailing vehicle immediately behind, the length of each of said first and second portions exceeding that of each vehicle; and control means aboard each vehicle connected to said receiving means thereof and responsive to said signal for arresting said drive means.
 2. A system as defined in claim 1 wherein said transmitting and receiving means are provided with antenna means for establishing between two vehicles a return path for said signals.
 3. A system as defined in claim 1, further comprising signal-responsive indicator means positioned next to said track and connected to at least one of said conductive elements for energization thereby upon passage of a vehicle thereover.
 4. A vehicular guidance system comprising: elongated guide means forming a track; a plurality of self-propelled vehicles provided with drive means and with sensing means for said track; transmitting means and receiving means for high-frequency electrical signals aboard each vehicle, said transmitting means being disposed on a first side and said receiving means being disposed on a second side of said track upon alignment of the vehicle therewith; a plurality of conductive strips disposed along said track in mutually insulated and longitudinally staggered relationship, each of said strips including a first portion extending alongside the track at said first side for energization by capacitive coupling with said transmitting means of a passing vehicle, a second portion extending alongside the track at said second side in capacitively coupled relationship with said receiving means of a passing vehicle, and a connecting portion crossing said track, said first portion preceding said second portion in the direction of vehicle motion and being substantially aligned with the second portion of an adjoining strip, said transmitting and receiving means being provided with respective antennas at opposite ends of each vehicle for establishing between two closely spaced vehicles a return path for said signals independent of said conductive strips; switchover means aboard each vehicle for making said transmitting and receiving means alternately effective in a predetermined rhythm different for each vehicle whereby a signal picked up by said first portion of any conductive strip from the transmitting means of a leading vehicle is communicated by said second portion thereof to the receiving means of a trailing vehicle immediately behind, the length of each of said first and second portions exceeding that of each vehicle; and control means aboard each vehicle connected to said receiving means thereof and responsive to said signal for arresting said drive means.
 5. A system as defined in claim 4 wherein said switchover means of different vehicles are pulse generators with harmonically related operating frequencies. 